Hello Rachel,
Take out the bobbin case then try the machine, if it is still tight it will be a matter of finding where it is tight, oil all moving parts with WD40, take the bottom off the machine and look at the nyon gear under the bobbin case area in case it has split, take the top off the machine and look at the nylon gear directly in front of you for any breaks.
Ken
drivewithken, May 2010